The present invention relates to an apparatus for the digging of ditches through rocky soils. In particular, the present invention relates to an apparatus for excavating hard soils and rock which operates by concentrating the force exerted by the apparatus against the hard soil at one or more specific points at any given moment so as to increase the ability of the apparatus to excavate the hard soil.
Ditching and excavating machines fall into two basic categories, the "power shovel" type and the "continuous ditcher" type. There are two basic types of continuous ditching and excavating machines, the "rigid wheel" and "chain" types.
The first continuous ditchers were rigid wheel machines, and were developed in very large sizes for use in such applications as the digging of irrigation canals. The more recently developed chain type of ditcher is smaller, more portable, more maneuverable and a more versatile unit. However, both wheel and chain types of ditchers penetrate hard soils poorly and are generally ineffective in massive rock formations. Excavation of massive, hard rock, requires the use of shovels or blasting in conjunction with shovels. Excavation of these harder soils with shovels or blasting has a number of disadvantages, the most serious being that shovel systems require a relatively large area in which to operate and that blasting may harm adjacent structures and is characterized by a great deal of noise and shock waves. There is, therefore, a need for continuous ditchers which are capable of excavating hard formations.
A commonly used type of chain ditcher is characterized by an elongated boom mounted on a supporting structure such as a tractor. The boom is pivoted to the tractor and is provided at both ends with a pair of sprockets, around which a heavy chain passes. The links of the heavy chain are provided with sockets welded to them in an orderly pattern such that when cutting teeth are placed in the sockets, the cutting surfaces of the teeth will cover the entire width of the ditch to be dug at least once in a complete revolution of the chain around the boom. Rotation of the chain as the boom is lowered causes the cutting teeth to abrade and chip away the material in front of the chain until the boom reaches the desired depth and cutting angle. The entire unit is then moved slowly forward so that the ditch is elongated at full depth in the direction taken by the tractor.
As the unit is moved forward, the cutting elements of the chain engage the entire face of ditch; that is, its entire "slant height" times the full width of the ditch. Only the tooth points actually touch the face of the ditch, but all the points on the chain along the entire face of the ditch are being advanced at the rate of the advance of the tractor, therefore, all the points are sharing approximately equal parts of the total effort available to rotate the chain and to advance the chain against the face of the ditch.
When each tooth's share of rotational chain pull and contact pressure is enough to give some pentration into the soil, rock will be chipped and routed from the face of the ditch and the ditching is accomplished at a meaningful rate. Chips and other spoil materials are lifted out of the ditch by the drag and impact forces imparted in an upward direction along the face of the ditch by the rapid rotation of the chain. However, if the rock is of sufficient hardness to resist the penetration of the teeth, the teeth slide along the surface of the rock instead of penetrating into it. The sliding of the teeth along the surface of the rock results in the abrasion of the rock rather than the ripping and cutting necessary for efficient elongation of the ditch. This abrasion generates a large amount of noise and dust and also increases the rate of wear on the cutting teeth.
Some improvement in efficiency has been provided by the redesign of the cutting elements. For instance, a current design utilizes a single point of tungsten carbide mounted on the link of the chain to give a good "claw" angle and to rotate in its socket so as to stay relatively sharp. Although this type of cutting element is less suceptible to the wearing caused by the sliding of the cutting element along the rock surface, the ditching process is still relatively slow, and the cutting elements do eventually wear out.
Another approach has been to use heavyweight units and traction systems capable of slipping the crawler tracks of the tractor upon which the ditching apparatus is mounted. Machines are currently available in the 90 ton class, but they are out of the price range of almost all general contractors, and in spite of their tremendous size and cost, do not represent a significant improvement.
A reduction in the number of cutting elements mounted on the chain links will increase the contact pressure of each of the remaining cutting elements. However, such a reduction concentrates all the wear on the remaining cutting elements, thereby reducing the average "redundancy" so that the loss of one or two cutting elements may require that the unit be shut down so that these cutting elements can be replaced. Further, there is a limit to the number of cutting elements which can be removed before the remaining cutting elements are incapable of excavating the entire surface of the ditch. For instance, approximately 30 cutting elements are required to adequately cover a ditch which is approximately 24 inches wide. In addition, even though each individual cutting element is more productive, the reduced number of cutting elements being employed and the greatly reduced spoil removal effects are disadvantages which effectively cancel the benefits of a reduction in the number of cutting elements.
It is, therefore, an object of the present invention to provide a ditch digging apparatus capable of excavating hard soils which is of similar size, weight, and traction to current ditching machinery. Another object of the present invention is to provide a ditch digging apparatus capable of excavating hard soils with a chain size, form and number of cutting structures which is equivalent to current ditching machinery. Another object of the present invention is to provide a ditch digging apparatus capable of excavating hard soils which is characterized by chain-drive horsepower, speed, and position controls which are similar to existing machinery.
It is another object of the present invention to provide a ditch digging apparatus in which a relatively large proportion of the tractive effort and rotating chain pull of the apparatus is applied to as few as two to four cutting elements at a given instant. It is also an object of the present invention to provide a ditch digging apparatus capable of excavating hard soils with cutting elements which are not worn away as quickly as those of currently available units.
Still another object of the present invention is to provide a boom for a ditch digging apparatus which is capable of excavating hard soils. Another object of the present invention is to provide a boom for a ditch digging apparatus in which the cutting force of the cutting elements of the apparatus is concentrated at one or more specific points along the apparatus at a given moment.